Helicopter preheat assembly

Abstract

A preheat apparatus for a helicopter wherein certain critical helicopter components are preheated preparatory to takeoff of the aircraft. The critical components include the main rotor gear case, the intermediate gear case, the tail rotor gear case, the oil tank and cooling assembly and the engine gear cases. In certain aircraft, these also include the fuel control unit and the drive reduction gear case. Heat pads are installed with respect to the critical components in strategic locations and are sized and shaped to fit the component. The heat pads are connected by wiring harness that is connected to an external source of electrical power.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A preheat apparatus for a helicopter of the type having a turboshaft engine with an engine accessory drive gear case, a main rotor gear case, a tail rotor gear case, an oil tank and coller assembly, and an intermediate gear case, said apparatus comprising: a first flat flexible electric heat pad, means installing the first head pad exteriorly on the engine accessory drive gear case at a lower portion thereof in position to supply heat to the accessory drive gear case and interior parts for maintenance of proper operating clearances;   a second flat flexible electric heat pad, means installing the second heat pad exteriorly on the main rotor gear case at a location in position to supply sufficient heat to the main rotor gear case and interior parts for maintenance of proper operating clearances;   a third flat flexible electric heat pad, means installing the third heat pad exteriorly on the tail rotor gear case in position to supply sufficient heat to the tail rotor gear case and interior parts for maintenance of proper operating clearances;   a fourth flat flexible heat pad, means installing the fourth heat pad exteriorly on the oil tank and cooler assembly;   a fifth flat flexible electric heat pad, means installing the fifth heat pad exteriorly on the intermediate gear case in position to supply sufficient heat to the intermediate gear case and interior parts for maintenance of proper operating clearances;   electric harness means interconnecting the first through fifth heat pads and having a main power lead connectable to an external source of electric power.   
     
     
       2. The preheat apparatus of claim 1 including: a pair of second heat pads installed on the main rotor gear case, and a pair of fourth electric heat pads installed on the oil tank and cooler assembly. 
     
     
       3. A preheat apparatus of claim 1 wherein: said fifth heat pad is fixed to the intermediate transmission gear case at a location beneath the lubricant level. 
     
     
       4. The preheat apparatus of claim 3 wherein: said first through fifth heat pads are comprised as flat members having a first layer of insulative material, a second layer comprised of an electrical heating element, and a third layer of insulative material joined edgewise to the first layer whereby the heating element is disposed between the first and third layers. 
     
     
       5. The preheat apparatus of claim 4 wherein: each of the first through fifth heat pads has a power-lead with a releasable plug connectable to the electrical harness means. 
     
     
       6. The preheat apparatus of claim 5 wherein: each of the first through fifth heat pads has a watt density not exceeding 10 watts per square inch. 
     
     
       7. A turboshaft engine helicopter preheat assembly for preheat of certain critical helicopter components preparatory to takeoff, said helicopter preheat assembly comprising: a plurality of critical helicopter components installed on a helicopter including an engine accessory gear case, a main rotor gear case, an oil tank and cooling assembly, an intermediate gear case, and a tail rotor gear case;   a first flat heat pad installed exteriorly on a first of said components;   a second flat heat pad installed exteriorly on a second of said components;   a third flat heat pad installed exteriorly on a third of said components;   at least two of said heat pads installed on gear cases in position to supply sufficient heat to the gear case and interior parts thereof for maintenance of proper operating clearances;   electrical harness means interconnecting the heat pads;   a main power lead connected to the electrical harness means and having an end extendible to an external source of electrical power for simultaneous energization of the heat pads.   
     
     
       8. The helicopter preheat apparatus of claim 7 including: a fourth heat pad installed on a fourth of said components; and a fifth heat pad installed on a fifth of said components. 
     
     
       9. The helicopter preheat apparatus of claim 8 wherein: said first through fifth heat pads have a power density not exceeding 10 watts per square inch. 
     
     
       10. A method of preheating a turboshaft engine helicopter at low temperature preparatory to takeoff comprising: installing a first flexible, flat heat pad on the engine accessory gear case of the engine on a lower portion thereof in position to supply sufficient heat to the accessory gear case and interior parts for maintenance of proper operating clearances;   a second flexible, flat heat pad on the main rotor gear case in position to supply sufficient heat to the main rotor gear case and interior parts for maintenance of proper operating clearances;   a third flexible, flat heat pad on the oil tank/cooler assembly below the oil storage level;   a fourth flexible, flat heat pad on the tail rotor gear case in position to supply sufficient heat to the tail rotor gear case and interior parts for maintenance of proper operating clearances;   a fifth flexible, flat heat pad on the intermediate transmission gear case in position to supply sufficient heat to the intermediate transmission gear case and interior parts for maintenance of proper operating clearances;   connecting the first through fifth heat pads with electrical harness means; and   simultaneously energizing the first through fifth heat pads by connecting the harness means to an external source of electricity.   
     
     
       11. The method of preheating a helicopter of claim 10 including: installing a heat pad on the fuel control unit and installing a heat pad with respect to the drive reduction gear case. 
     
     
       12. A method of preheating a turboshaft engine helicopter of the type having as critical components an engine accessory gear case; a main rotor gear case; an oil tank and cooling assembly; an intermediate gear case; and a tail rotor gear case comprising: installing a first flexible, flat heat pad on a first of said components;   installing a second flexible, flat heat pad on a second of said components;   installing a third flexible, flat heat pad on a third of said components, wherein at least two of said heat pads are positioned to supply sufficient heat to gear cases and interior parts thereof for maintenance of proper operating clearances;   connecting the first, second and third heat pads with wiring harness means and supplying electrical power to the wiring harness means.   
     
     
       13. The method of preheating a helicopter of claim 12 including: installing a fourth heat pad on a fourth of said components; and installing a fifth heat pad on a fifth of said components; and connecting the fourth and fifth heat pads to the wiring harness means. 
     
     
       14. The method of preheating a helicopter of claim 12 wherein said helicopter also has as critical components a fuel control unit and a drive reduction gear case, and including: installing a fourth heat pad on a fourth of said critical components. 
     
     
       15. The method of preheating a helicopter of claim 14 including the step of: installing a fifth heat pad on a fifth of said components and connecting said fifth heat pad to the wiring harness means. 
     
     
       16. A preheat apparatus for a helicopter of the type having a turboshaft engine with an engine accessory drive gear case, a main rotor gear case, a tail rotor gear case, an oil tank and cooler assembly, and said apparatus comprising: a first flat flexible electric heat pad, means installing the first heat pad exteriorly on the engine accessory drive gear case at a lower portion thereof in position to supply heat to the accessory drive gear case and interior parts for maintenance of proper operating clearances;   a second flat flexible electric heat pad, means installing the second heat pad exteriorly on the main rotor gear case at a location in position to supply sufficient heat to the main rotor gear case and interior parts for maintenance of proper operating clearances;   a third flat flexible electric heat pad, means installing the third heat pad exteriorly on the tail rotor gear case in position to supply sufficient heat to the tail rotor gear case for maintenance of proper operating clearances;   a fourth flat flexible heat pad, means installing the fourth heat pad exteriorly on the oil tank and cooler assembly;   electric harness means interconnecting the first through fifth heat pads and having a main power lead connectable to an external source of electric power.   
     
     
       17. The helicopter preheat assembly of claim 16 wherein said helicopter includes a fuel control unit and including: a fifth flat flexible electric heat pad, means installing the fifth heat pad on the fuel control unit. 
     
     
       18. A method of preheating a turboshaft engine helicopter at low temperature preparatory to takeoff comprising: installing a first flexible, flat heat pad on the engine accessory gear case of the engine on a lower portion thereof in position to supply sufficient heat to the accessory gear case and interior parts for maintenance of proper operating clearances;   a second flexible, flat heat pad on the main rotor gear case in position to supply sufficient heat to the main rotor gear case and interior parts for maintenance of proper operating clearances;   a third flexible, flat heat pad on the oil tank/cooler assembly below the oil storage level;   a fourth flexible, flat heat pad on the tail rotor gear case in position to supply sufficient heat to the tail rotor gear case and interior parts for maintenance of proper operating clearances;   connecting the first through fourth heat pads with electrical harness means; and   simultaneously energizing the first through fourth heat pads by connecting the harness means to an external source of electricity.